80 
ZOOLOGICAL GEOGRAPHY. 
[PART III, 
conditions, of once wide-spread groups. If no wild species 
of the genus Equus were now to be found, except in South 
Africa (where they are still most abundant), and in South 
Temperate America, where their fossil remains show us they did 
exist not very long ago, what a strong fact it would have 
appeared for the advocates of continental extensions! Yet it 
would have been due to no former union of the great southern 
continents, but to the former extensive range of the family or 
the genus to which the two isolated remnants belonged. And if 
such an explanation will apply to the higher vertebrata, it is 
still more likely to be applicable to similar cases occurring among 
insects or mollusca, the genera of which we have every reason to 
believe to be usually much older than those of vertebrates. It 
is in these classes that examples of widely scattered allied 
species most frequently occur ; and the facility with which they 
are diffused under favourable conditions, renders any other 
explanation than that here given altogether superfluous. 
The Solenodon is a member of an order of Mammalia of low 
type (Insectivora) once very extensive and wide-spread, but 
which has begun to die out, and which has left a number of 
curious and isolated forms thinly scattered over three-fourths of 
the globe. The occurrence, therefore, of an isolated remnant of 
this order in the Antilles is not in itself remarkable ; and the 
fact that the remainder of the family to which the Antillean 
species belong has found a refuge in Madagascar, where it has 
developed into several distinct types, does not afford the least 
shred of argument on which to found a supposed independent 
land connection between these two sets of islands. 
Summary of the Past History of the Neotropical Region. 
We have already discussed this subject, both in our account 
of extinct animals, and in various parts of the present chapter. 
It is therefore only necessary here, briefly to review and sum- 
marise the conclusions we have arrived at. 
The whole character of Neotropical zoology, whether as regards 
its deficiencies or its specialities, points to a long continuance 
of isolation from the rest of the world, with a few very distant 
